Those who walked briskly for at least 1 hour per day attenuated their genetic predisposition to obesity, according to results of a study presented at the American Heart Association’s Epidemiology and Prevention/Nutrition, Physical Activity and Metabolism 2012 Scientific Sessions.

In contrast, those who followed a sedentary lifestyle that included prolonged TV watching accentuated their genetic disposition to obesity and increased BMI, researchers found.

The study included longitudinal data from 7,740 women who participated in the Nurses’ Health Study and 4,564 men from the Health Professionals Follow-up Study. Researchers collected data on physical activity and TV habits 2 years before assessment of BMI. Genetic predisposition score was calculated on the basis of 32 established BMI-predisposing variants. The effect of genes on obesity was measured by differences in BMI per point of the genetic predisposition score, corresponding to each BMI-increasing gene, according to a press release.

Each BMI-increasing gene was associated with a 0.13 kg/m² increase in BMI. This effect was reduced in those with the highest level of physical activity compared with those with the lowest (0.08 kg/m² vs. 0.15 kg/m²; P<.001). The genetic effect on BMI was more pronounced in those who spent more than 40 hours per week watching TV compared with those who watched 1 or fewer hours per week (0.34 kg/m² vs. 0.08 kg/m²; P=.001).

One hour of brisk walking per day was associated with a 0.06 kg/m² reduction in the genetic effect on BMI. Each 2-hour per day increment in TV watching was associated with a 0.03 kg/m² increase in genetic effect on BMI, according to the results.

For this study, obesity was defined as a BMI of at least 30.

“Our data suggest that both increasing exercise levels and reducing sedentary behaviors, especially TV watching, independently may mitigate the genetic predisposition to increased BMI,” Qibin Qi, PhD, postdoctoral research fellow in the department of nutrition at Harvard School of Public Health, and colleagues concluded.

How the function of these genes affect BMI is not clear, according to Qi.

“These genes were just identified in the past 5 years and the exact functions of the genetic variants are still unknown,” he said in a press release. “Future studies will be needed to uncover the underlying mechanisms.”

It is reasonable to assume that people who are going to be more physically active are going to be less obese. Certainly, we are learning a lot more about the negative impacts of sedentary behavior, and are using TV time as a reasonable correlate of sedentary behavior. The take-home message is that there are genes that predict propensity for obesity, but, in the case of obesity, genes are not destiny. Essentially, physical activity behavior can play an important role in the majority of patients to help them stay at an ideal body weight despite having gene profiles that are predisposed to become obese. It emphasizes the very importance of physical activity lifestyle and avoiding obesity.

– Richard A. Stein, MD
Professor of Medicine
New York University

Source:Endocrine Today.